A crucial part of the transceiver function (TRU) in a radio base station (RBS) is the power amplifier (PA). The TRU dissipates a great quantity of heat when transforming signals from the telephone exchange to the antenna and further out to cellular phones etc. The radio frequency power transistors generate most of the heat quantity, but also other components such as radio application specific circuits (RFASIC) are generating heat. The total of the heat quantity might be difficult to transfer to the surrounding atmosphere via the cooling fins, which usually are arranged on the outside of the shielding box that that surrounds the electronics.
The use of so called thermal vias is one previously known technique to conduct heat through a printed circuit board (PCB). A via is usually a small copperplated hole or barrel in the PCB, which is positioned beneath a heat-dissipating component. Several holes might be needed to achieve a good thermal path from a component to the cooling fins. The design of a component package is often such that a heat pad is available on the bottom of the package. This heat pad is by solder material connected to the copper pad on the PCB and through the copperplated vias to the cooling fin arrangement.
One problem with this technique that might occur is that solder droplets easily appear on the bottom side of the PCB during the soldering process. This implies that it might not be possible to fasten the PCB tight with the fin arrangement, which would cause a bad thermal path. This in turn might cause damage to the components due to severe overheating and unintentional bending of the PCB. In addition, the thermal conductivity of a copperplated via is relatively low, which limits this traditional method to an effective output of approximately 10 W.
Apparently, there has been a need for making modifications of printed circuit boards to decrease the thermal resistance from one side to another of said boards and to reduce the appearance of solder droplets on the opposite side of the board relative to the component body.
Also, it has been proposed to make said modifications by integrating copper inserts in the PCB to achieve an effective output of up to ten times more compared to what can be ac+hieved by means of the traditional method. The copper inserts also effectively hinder the appearance of solder other than in the joint position.
In each of SE 0004894-2 and PCT/SE00/01349 (WO 01/01738), which have been filed with the same inventor and applicant as in the present application, is described a method of providing modified thermal vias in a printed circuit board of the above mentioned kind and a printed circuit board that includes vias arranged in accordance with the aforesaid method.
One problem involved in providing modified printed circuit boards is that, information taken, hitherto it has been quite time consuming and complicated to achieve the advantages afforded by the above patent applications in manually performed steps for each modified PCB. Therefore, it would be desirable to make said modifications automatically and preferably by a means arranged to integrate said copper inserts in the PCB as a natural process step during the PCB fabrication.